Shimming procedure that includes determination of the target field by optimization in a parameter space of reduced dimensionality

摘要

A static B0 field is actively shimmed by mapping the field distribution, defining a target distribution and setting shim currents. An optimising procedure is used to define the target distribution, such as Tikhonov regularisation, truncated single value decomposition (TSVD) or damped single value decomposition (DSVD). At least two parameters are used to control the optimisation including a regularisation parameter and a weighting parameter for a spatial weighting function, with one parameter described as controlling filter factors in a filter methods used as the optimising procedure. A quality criterion is optimised by the method to select the target distribution. Evaluation of feasible current settings is also part of the method based on lists of values for weighting and regularisation parameters with a numerical quality criterion value determined for each.